Base-free synthesis of benchtop stable Ru(III)-NHC complexes from RuCl 3 ·3H 2 O and their use as precursors for Ru(II)-NHC complexes.

A series of Ru(III)-NHC complexes, identified as [Ru(PyNHC)(Cl)(HO)] (1a-c), have been prepared, starting from RuCl·3HO following a base-free route. The Lewis acidic Ru(III) centre operates a halide-assisted, electrophilic C-H activation for carbene generation. The best results were obtained with azolium salts having the I anion, while ligand precursors with Cl, BF, and PF gave no complex formation and those with Br gave a product with mixed halides. The structurally simple, air and moisture-stable complexes represent rare examples of paramagnetic Ru(III)-NHC complexes. Furthermore, these benchtop stable Ru(III)-NHC complexes were shown to be excellent metal precursors for the synthesis of new [Ru(PyNHC)(Cl)(PPh)] (2a-c) and [Ru(PyNHC)(CNC)I]PF (3a-c) complexes. All the complexes have been characterised using spectroscopic methods, and the structures of 1a, 1b, 2c, and 3a have been determined using the single-crystal X-ray diffraction technique. This work allows easy access to new Ru-NHC complexes for the study of new properties and novel applications.